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Taikichiro Mori Memorial Research Fund

Graduate Student Researcher Development Grant Report

Name : Vu Thi Huong Giang
Student ID : 80825490
Supervisor : Prof.
Hideyuki Tokuda

Research Topic

iPATH: Achieving high-performance end-to-end paths for multi-homed
mobile hosts

Mobile users desire to always connect to the network that
provides the highest transmission performance. None of wireless access networks
today; including GPRS, 3G, WiMAX and WLAN, can satisfy all the requirements of
users, because their characteristics are trade-off in terms of available
bandwidth, wireless coverage and power consumption. For example, WLAN provides
high bandwidth in a small coverage while 3G networks support wide range mobility
with low transmission speed. However, those heterogeneous wireless networks
coexist and their characteristics perfectly complement each other. With the
advancement of multiple-interface mobile devices (e.g., smart phones, netbooks),
users now have the chance to utilize their preferred networks with vertical
handoff between their multiple, distinct network interfaces.

In
traditional handoff mechanisms, handoff only occurs when current serving network
becomes unreachable or its signal quality falls below threshold to satisfy the
communication quality. Received-Signal-Strength (RSS) and other parameters
obtained from the wireless signal are therefore decisive indicators for the
threshold to execute handoff. However, these parameters are not sufficient for
selecting an access network which provides the highest performance. End-to-end
path conditions, including available bandwidth, delay, packet loss rate and
jitter affect the communication performance in addition to the wireless signal
condition. Thus, interface selection or handoff decision based on these
end-to-end parameters could significantly improve communication performance.

In addition, cost for handoff or ``switching cost'' is important for
handoff decision. Handoff reduces transport protocol performance due to
resetting congestion control parameters, such as congestion window, which takes
time to reach the previous sending rate again from the initial window size. This
behavior also increases transmission jitter, which is problematic for
applications that prefer smooth transmission. For these reasons, inefficient
handoff should be avoided. In other words, decision to execute handoff in
end-system should be done with the considering if it pays the switching
cost.

In this research, we design and implement an intelligent vertical
handoff system named iPath, which maintains a high-performance end-to-end path
for multi-homed mobile hosts. iPath is an end-to-end system, hence it does not
require any modification to the network infrastructure. iPath has two advantages
to existing work:

The highest-performance end-to-end path: iPath can ensure the highest
performance end-to-end path, because it selects the path based on end-to-end
measurement.

Minimized handoff overhead: iPath can minimize performance degradation
caused by handoff execution, because it makes handoff decision with the
consideration to switching cost.

iPath provides two functionalities to
achieve these advantages. First, iPath collects end-to-end path properties
including available bandwidth, delay, packet loss rate and transmission jitter
by end-to-end path measurement from each local network interface. Second, iPath
selects the highest-performance path based on the switching cost in addition to
end-to-end path properties. Path selection of iPath is implemented as extensions
of some widely used handoff decision algorithms.iPath provides two
functionalities to achieve these advantages. First, iPath collects end-to-end
path properties including available bandwidth, delay, packet loss rate and
transmission jitter by end-to-end path measurement from each local network
interface. Second, iPath selects the highest-performance path based on the
switching cost in addition to end-to-end path properties. Path selection of
iPath is implemented as extensions of some widely used handoff decision
algorithms.

Research results

We built an iPath prototype system which's transport layer
protocol is SCTP in an IBM X30 computer and tested this system in a real network
environment. We gained good results as follow:

The adopted switching costs prevent ineffective handoff in all tested
algorithms: In this research, we adopt switching cost to 3 widely used handoff
algorithms: TOPSIS, SAW and Hongwei Liao's. The experiment results show that
those algorithms with adopted switching cost have higher accuracy in choosing
high-performance end-to-end paths.

Interface switching which is based on end-to-end parameters considerably
improves network performance: As in our experiment, handoff system which uses
end-to-end paramters as handoff trigger can improve network performance
(transmission time of application) up to 30% .

Future work

Complete the implementation of the system so that it can runs with all
transport layer protocol

Improve the overhead and measurement accuracy of Path property retrieval
module.

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